There's a huge amount you can do yourself. My husband and I aren't trades, although I was a welder and he's an engineer. I teach now and he punches keys, so it wasn't really in our skill set. We are on the third house now. We can paint, tile, demolish, point, plumb, fit a kitchen, cut worktops, like for like electricals, chase walls, hang doors, fit skirting, basically anything that isn't structural or you need to be licensed for eg gas. Trades will do it much faster and won't take 4 attempts but you can save a fortune. Only thing I can't do is plaster. I can patch but...it's not excellent. We got the Collins DIY manual and learned as we went. First couple of things were pretty bad, but now we're pretty good. We had some electricians in rewiring, and I was building a staircase. You say you'll bever use SOHCAHTOA from maths in real life...but that's how I built my stairs.